Prior art winches which are operated by motors powered by air or other pneumatic fluids usually includes limit stops which limit the travel of the winch at its upper and lower points. These limit stops usually take the form of a normally open valve in the working fluid line immediately before the winch motor; when the limit stop is reached, another valve is opened which sends pilot fluid to the normally open valve which closes the valve thereby stopping the winch motor.
This type of limit stop arrangement works well unless there is a leak or break in the pilot fluid line leading to the valve in the working fluid line. When there is a leak or break in the pilot line, pilot fluid does not reach the valve and the valve does not close; thus the winch motor continues to turn, and the winch exceeds its limits of travel. This results in damage to the winch, other equipment, or personnel in the area.
Electrically operated limit switches are generally not feasible, since pneumatic powered equipment is usually used in those environments where the possibility of an electrical spark can not be tolerated. The use of an electric limit switch system would cancel out the safety feature of using the pneumatic powered winch rather than an electric powered winch.
The present invention is a valving arrangement for a pneumatic powered winch which eliminates the above drawback.